Seed relay: a stalled compressed XOVER is fetched again uncompressed

The four ranges kept failing on fresh connections too: in gzip mode Eweka
stops some chunks partway (a.b.ath 49701720000: 19,672 of 20,000
overviews, the last line cut, then silence), while the same chunk without
compression comes in 0.3 s. A failed relay chunk is now retried once
without compression on a connection of its own (dead pooled connections are
covered by the same retry).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/unit/seed_fetch_pool.spec.ts

@@ -7,8 +7,9 @@ import SeedFetchPool from '#services/SeedFetchPool'
 import { parseOverviews } from '#lib/nntp/xover_client'
 
 test.group('SeedFetchPool', () => {
-  test('a chunk that fails on a dead connection is fetched again on a fresh one', async ({ assert }) => {
+  test('a chunk that fails (dead connection, stalled compressed reply) is fetched again uncompressed', async ({ assert }) => {
     let connections = 0
+    const compressAsked: Record<number, boolean> = {}
     const server = net.createServer((sock) => {
       const n = ++connections
       sock.write('200 welcome\r\n')
@@ -16,7 +17,7 @@ test.group('SeedFetchPool', () => {
         for (const line of chunk.toString().split('\r\n').filter(Boolean)) {
           if (line.startsWith('AUTHINFO USER')) sock.write('381 more\r\n')
           else if (line.startsWith('AUTHINFO PASS')) sock.write('281 ok\r\n')
-          else if (line.startsWith('XFEATURE')) sock.write('500 no\r\n')
+          else if (line.startsWith('XFEATURE')) (compressAsked[n] = true), sock.write('500 no\r\n')
           else if (line.startsWith('GROUP')) sock.write('211 1 7 7 a.b.test\r\n')
           // The first connection dies as the request arrives, like one the server dropped while idle.
           else if (line.startsWith('XOVER') && n === 1) sock.destroy()
@@ -32,6 +33,8 @@ test.group('SeedFetchPool', () => {
       const raw = await SeedFetchPool.fetch('a.b.test', 7, 7)
       assert.deepEqual(parseOverviews(unzipSync(raw).toString('utf8')).map(([n]) => n), [7])
       assert.equal(connections, 2)
+      // The pooled connection asked for gzip; the retry didn't.
+      assert.deepEqual(compressAsked, { 1: true })
     } finally {
       SeedFetchPool.closeIdle()
       Object.assign(nntpConfig, { host: saved.host, port: saved.port, secure: saved.secure })